With increasing oxidative stress, oxygen free radicals attack esterified arachidonate layered within cell membrane lipid bilayers, resulting in the production of multiple lipid peroxidation products called isoprostanes (Iso-P) and isofurans (IsoF) (13-17). Many forms of IsoF and IsoP have been shown to be powerful vasoconstrictors, and have been shown to contribute to the pathogenesis and organ dysfunction associated with rhabdomyolysis, subarachnoid hemorrhage and hemolytic disorders (10, 16, 18-21). F2-isoprostanes are sensitive and specific markers of oxidative stress in vivo. (4) The mechanism/s causing increased oxidative stress during CPB are incompletely understood and the relationship between free hemoglobin and F2-isoprostanes in humans undergoing CPB is unknown.